The passenger in question was a Dr, who was needed at a hospital in Louisville the next morning. Even if the normal arguments about having booked your seat don't sway you, this is a perfectly good reason to resist being thrown off.
Like someone else said, they should have auctioned the seats and upped the price until someone volunteered. This is normal practice and happens all the time. Disgraceful behaviour, I hope they have the book thrown at them.